Res. Inst. of Logopedics and Phoniatrics, Faculty of Medicine, Univ. of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113 Japan
Tokyo Gakugei Univ., 4-1-1, Nukui-kita-machi, Koganei, Tokyo, 184 Japan
Listener adaptive characteristics of Japanese vowel devoicing in dialogue were investigated by analyzing dialogue between teachers and hearing-impaired (HI) or normal-hearing (NH) children. Dialogue was recorded during a game through which seven teachers assessed the speech perception of seven hearing-impaired and seven normal-hearing children. The following results were obtained. (1) Devoicing rate was significantly lower in dialogue directed to HI than to NH. (2) For vowel /i/ in the second mora of /CVkita/, where C was one of /h,s,sh,ts/ and V /i,u/, unvoiced segments of not-fully-devoiced syllables that were mainly directed to HI tended to be shorter than those of fully devoiced syllables that were mainly directed to NH. This may indicate that the teachers avoided devoicing by shortening unvoiced duration and lengthening voiced duration for HI. (3) Monosyllables and pauses in dialogue directed to HI were longer than those directed to NH. These results suggest that the teachers controlled their speaking style to help the hearing-impaired to understand dialogue by avoiding or reducing vowel devoicing.